William Crookes

Sir William Crookes was an English chemist and physicist, born in London on 17 June 1832 and died on 4 April 1919, who attended the Royal College of Chemistry and worked on spectroscopy. He was a pioneer of vacuum tubes and invented the Crookes tube, made in 1875, and observing the cathode rays in such tubes he posited radiant matter as a fourth state of matter, a foundational contribution to plasma physics. He is credited with discovering the element thallium, announced in 1861, and was the first to describe the spectrum of terrestrial helium in 1865. He also invented the Crookes radiometer, a light driven device that later became a physics classroom demonstration of a heat engine.